Missoula, Montana: Teenagers call it garage hopping. The goal was to sneak into an open garage, steal some beer or other items and slip away into the night.

It was dumb and clearly illegal. It was not supposed to be deadly.

Around midnight on April 27, a 17-year-old exchange student from Germany named Diren Dede left his host home with a friend. They passed a home whose garage door hung partially open. Using a mobile phone for light, Dede headed in.

Last moments: Diren Dede, a German exchange student, is seen on a baby monitor just before he was shot and killed by Markus Kaarma after entering Mr Kaarma's garage in Missoula on April 27. Photo: New York Times

Inside the house, motion sensors alerted Markus Kaarma, 29, to an intruder's presence. Two recent burglaries had put Mr Kaarma and his young family on edge, his lawyer said, and he grabbed a shotgun from the dining room and rushed outside.

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He aimed into the garage and, according to court documents, fired four blasts into the dark. Dede's body crumpled to the floor.

While Mr Kaarma has been charged with deliberate homicide, Dede's death has set off an outcry an ocean away in Germany, exposing the cultural gulf between a European nation that tightly restricts firearms and a gun-loving Western state.

'This is not us': Kate Walker and Randy Smith, the host family of slain exchange student Diren Dede, attend a vigil for him in Missoula, Montana, on May 2. Photo: New York Times

In his defence, Mr Kaarma is expected to turn to laws enacted in Montana five years ago that allow residents more legal protections in using lethal force to defend their homes.

In an interview with a German news agency, Dede's father criticised what he called an American cowboy culture as contributing to his son's death. In Dede's hometown, Hamburg, hundreds of his stunned relatives, friends and soccer teammates attended memorials, holding photos of Dede and unfurling a banner that read: "Our brother is dying while America is looking on."

In Montana, which has one of the country's highest rates of gun ownership, the killing has renewed criticism of the state's "castle doctrine" laws, which allow residents wider latitude to use force to defend their homes.

Nearly every state has a law on the books giving residents the legal right to defend their homes, but Montana is among several that have gone further. With backing from the National Rifle Association and the support of the state's Democratic governor, Montana passed a law in 2009 that placed the burden on prosecutors to rebut claims of self-defence.

Under the old laws, residents were justified in using force only if an assailant tried to enter their home in a "violent, riotous or tumultuous manner". The new law eliminates that language and makes it clear that residents can use force if they reasonably believe it is necessary to prevent an assault on themselves or someone else in the home.

These laws are expected to play a crucial role in the criminal case that has been filed against Mr Kaarma, who is out on bail and is to be arraigned on Monday. His lawyer, Paul Ryan, says Mr Kaarma feared for his family's safety and panicked.

State congresswoman Ellie Boldman Hill has proposed repealing the castle laws, saying that they have fostered a shoot-first culture in Montana.

"I'm a liberal legislator from Montana, and I have a handgun in my closet," she said. "We are proud of our gun-owning tradition, but enough is enough. It's like a licence to kill. People are walking around exercising vigilante justice."

Steve Daines, a Republican congressman running for the US Senate, recently told a veteran's group he supported the laws as they stand, a view echoed by gun enthusiasts. His opponent, Senator John Walsh, a Democrat, supports them as well.

Gary Marbut, president of the Montana Shooting Sports Association, said: "I think it's working just fine."

In times of emergency in Montana, Mr Marbut said, the police are often an hour's drive away. "Self-defence is a natural right. It is part of the nature of being a free person that your life has value and you can protect that life."

But in Missoula, a liberal college town ringed by snow-capped peaks, Dede's classmates and neighbours as well as other residents have expressed sympathy for him and tried to distance their community from the bloody events of that night.

Scores attended a candlelight vigil for Dede, and ribbons bearing the red, gold and black of the German flag hang around nearly every mailbox post in his neighbourhood.

"This is not us," said Randy Smith, one of Dede's host parents. "It's not our neighbourhood, it's not our country. It's not Montana."

Two recent burglaries had made Mr Kaarma and his partner, Janelle Pflager, feel like targets inside their home, Mr Ryan said. Someone had entered their open garage - the couple kept it open so they could duck out to smoke cigarettes - and stolen a wallet and credit cards. The couple are first-time parents with a 10-month-old.

Ms Pflager bought motion sensors and a video camera to track the intruders should they return, and put a purse with some marked belongings inside, so that they could be traced to anyone who stole them.

A hairstylist named Felene Sherbondy told the police that Mr Kaarma had come into the Great Clips salon three days before the shooting and talked about how he had been waiting up with his shotgun for three nights "to shoot some kid". Ms Sherbondy told the police that Mr Kaarma was being "extremely vulgar and belligerent".

Mr Kaarma told the police that in the moments before Dede's death, he heard the sound of metal touching metal as he stared into the pitch-black garage, and swept the gun across the width of the garage as he fired. Ms Pflager told the police she heard a few yells of "Hey!" or "Wait!" from inside the garage, and then gunshots. It all happened in less than 10 seconds, the couple told the police.

The friend accompanying Dede that night, an exchange student from Ecuador, stayed outside the home.

Dede's host parents, Mr Smith and Kate Walker, who say they have never locked their doors and have never been burgled, have spent the last week grieving for a 17-year-old who had begun to feel like a family member.